Generally, toners are used for the development of electronic photographs, electrostatic printers, copying machines, etc. and refer to pigments used for the development of pictorial images in printed materials during the printing work. It has been the actual situation that the demand for image-formation devices such as printers, etc. has been increased rapidly, and consequently, the amount of use of toners has been increased as the preparation for documents using computers and similar works has been generalized recently.
There are many methods of manufacturing toners. In the melting-mixing process, which is the most widely known general method, resins and pigments are put together, melted and mixed or extruded, and pulverized and classified in order to manufacture toner particles. However, the toner particles manufactured according to the above process have been problematic in their charging or flowing property since they have a wide distribution of particle sizes and very irregular shapes such as sharp edges, etc.
In order to resolve the above problem, methods of manufacturing spherical toner particles according to the polymerization method have been presented. As concrete methods by the above polymerization method, emulsion polymerization method and suspension polymerization method have been known. At present, the suspension polymerization is preferred since the emulsion polymerization is more complicated process.
The method of manufacturing toners by the suspension polymerization is disclosed in the U.S. Pat. No. 6,337,169. What is claimed in this patent is that the pigment included in a wax forms pictorial images promptly with the wax since the wax is melted promptly when the toner is fused at a high temperature if only the fixed part of a pigment is melted in the wax, thus enabling the formation of high-quality pictorial images. The structure of the wax at that time is in one or a few large spherical shapes in the central binder portion, and is in the sea-island-sea shape on the whole. However, in order for the wax to have such structure, the type of the wax used for the binder has to be limited. Further, there have been problems that the fixed part of the pigment in the toner has been melted in the wax, and the remainder has been dispersed in the binder, or all of the pigments are dispersed evenly in the binder; and the charge control agent, assuming the most important role in the charging characteristics of toners, has failed to have been located at the outer side efficiently as well. Still further, there has remained the problem of excessive absorption of moisture according to the increased amount of charging although the amount of an electric charge on the surface of toners is increased.
In other words, in order to form high-quality pictorial images, the development of toner particles, capable of increasing the surface concentration of the charge control agent in the toners irrespective to the type of the wax and stopping the subsequent absorption of moisture, has been demanded continuously.